Protective device for transformers



Feb. 20, 1951 R. H. SEAMAN PROTECTIVE DEVICE FOR TRANSFORMERS Filed Nov.13, 1945 INI "ENT OR. "W72 1' 1:12 arc! 1 55 51121011 BYM MM i HI /.5

Patented Feb. 20, 1951 UNITED STATES PATENT OFFICE PROTECTIVE DEVICE FORTRANSFORMERS;

Richard H. Seaman, Los Angeles, Calif.

Application November 13, 1945, Serial No. 628,191

4 Claims. 1

This invention relates to the provision of means primarily designed toprotect electrical transformers of the step-up type from injury in theevent that the secondary circuit of the transformer becomes accidentallyopened.

The invention is hereinafter described as particularly applied totransformers used in neon sign work, although. the scope of theinvention is not necessarily solimited.

Transformers used in gaseous discharge tube circuits, and particularlyin connection with neon tube signs, are of the, high voltage. type, thesecondary voltage being. usually of the order of H. 15. 0 o ts. Al h ugt i e er practice to. provide transformers of the high leakage type forsuch use, the accidental break-.- in of the sign.v whi s a ommo ccurence. W111 nevertheless ause. hi h. v ta es to bu ld p in the secondaryWinding of the transformer with the result that, if the circuit is notpromptly disconnected the transformer is apt to become overheated andruined or cause fires It is therefore advantageous to provide protective devices for such signs which will act practicallyinstantaneously to interrupt the electrical power supply to thetransformer. Such devices, for maximum safety, should operate if eitherside of the high tension circuit becomes open or accidentally grounded.

Also since it is frequently necessary to re place gaseous dischargetubes, and such replace;

ment may be. attempted by) unskilled persons,

art cularly n indoor i l at ons nv i h a eous i arge. ub s ar lik y to bof he hot cathode high current type, serious injury from electricalshock may be experienced by contacting the socket terminals with thefingers if the person attempts to fit a new tube in the sockets withoutfirst turning off the current. By the use of the device of thisinvention the current is cut off from the tube circuits as soon as thesecondary or high voltage circuit is interrupted either by breaking ofthe tube or removal thereof from the socket without first turning offthe current so that electric shocks cannot beexperienced.

The peak voltages used in neon sign work are necessarily high in orderto provide the striking o t o the ub w c m be 2 c mo e in exces of thenprmal operating voltage. The brief application of such voltage in thetransformer previous to lighting of the sign does not harm thetransformer since the voltage drops immediately the sign is lighted, butthe generation of this. gh; olta e or considerable 2 period of time,should the sign be broken, will damage the transformer.

Neon signs are very commonly erected on the roadside or in relativelyinaccessible places, such as on roof tops and the like, and aconsiderable period of time may elapse before the sign is visited formaintenance or the inoperativeness of the sign is noticed. Largevnumbers of transformers are used in connection with such, gaseousdischarge tube signs, both because of the great number of such signs andbecause large signs are commonly built u of separate sections, eachprovided with its own transformer, so that the cost of replacement ofdamaged transformers constitutes a relatively heavy item in themaintenance of such signs.

It is an object of the invention to protect transformers, particularlyof the high voltage type used with gaseous discharge tubes. such as neonsigns, by the provision of an inexpensive device which will act tointerrupt the primary c rcuit of the, transformer should the secondarycircuit be accidentally opened.

It is a further object of the invention to provide a device of the kinddescribed which is simple in construction and inexpensive to manu-.facture.

A further object of the invention is to provide a device of the kinddescribed which may very readily be replaced if necessary.

Another object of the invention is to provide a protective device forthe purpose descr bed havin; no moving parts and therefore free fromdeterioration due to mechanical wear.

A further object of the invention is to provide a protective device forthe purpose described which is actuated by the ionization of gas in agaseovs discharge tube to cause arcing across e'ectrodes shaped andarranged to reduce to a minimum wear on the electrodes caused by the areso that the device is practically free from deterioration due to theeffect of the are.

A further object of the invention is to provide a method of protectingtransformers from damage due to bu lding up of excessively high voltagein the secondary winding thereof.

Further features and objects of the invention will hereinafter appear inthe following descrip-. tion taken in conjunction with the accompanyingdrawings, in which Fig. 1 is a diagram showing the connection of theprotective device in a circuit including a transformer, in which oneelement is connected to one side. of the secondary of the transformer;

Eig. 2 is a diagram shqwing; the protective de.-.

vice having elements connected to both sides of the secondary of thetransformer;

Fig. 3 is an elevation of the protective device shown diagrammaticallyin Fig. 1 and drawn to a larger scale;

Fig. 4 is a side elevation of the protective device diagrammaticallyshown in Fig. 2; and

Fig. 5 is a plan view of the device shown in Fig. 4.

Referring now to Fig. 1, the primary of the transformer is indicated bythe numeral [0 and the secondary by the numeral [2. An overload fuse I4of the usual type is provided in the transformer primary circuit as iscustomary.

The protective device of my invention is indicated by the numeral IS.The device comprises an envelope I8, which may be a length of glasstubing in which is sealed a suitable gas, such as argon or neon, at asuitable low pressure.

Two electrodes 20 and 22, preferably of platelike form closely spaced,are sealed into the glass envelope to provide a spark gap, the distancebetween the electrodes being such that the normal maximum workingpotential of the secondary is insufficient to establish an arc betweenthe electrodes. Electrode 22 is connected to one side of the primarywinding by lead 59 and the other electrode 20 is connected to the otherside of the primary winding by lead 2 I.

A third electrode 24, in the form of the device shown in Fig. 3, issealed into the upper end of the glass envelope and may be connectedthrough the metal cap 25 and lead 2'! into one side of the secondarywinding I2 of the transformer.

Should the secondary circuit of the transformer become opened, forinstance, by the breaking of the neon sign, excessive voltages will bebuilt up in the secondary, resulting in ionization taking place betweenelectrode 24 and electrode 20 (or electrode 22) which reduces theresistance of the gas path between electrodes 20 and 22 thereby causingconduction from electrode 20 to 22 (or from 22 to 20) in parallel to theprimary winding of the transformer. The current from this parallelcircuit flowing through the fuse I 4 will burn out the fuse. Onceconduction takes place from electrode 20 to 22 (01' from 22 to 20),conduction ceases from electrode 24 to electrode 20 (or 22).

When an arc is established the primary winding ID of the transformer isof course directly shorted, causing the protective fuse 14 to blow,thereby disconnecting the transformer from the power lines andpreventing any damage thereto.

It will be noted that the protective device l6 can be formed to bereadily inserted in a socket 26. the tube l8 being formed with a basefurnished with a pin 28 engaging a slot 30 in the socket 28. Electrodes20 and 22 may be furnished with pins 32, 34 projecting through the baseand engaging with metal strips 36, 38, making contact with screw topterminals 40, 42 to which the leads I9 and 2| may be attached.

In the form of the device shown in Figs. 4 and 5, two electrodes 44, 46are provided and are connected one to each side of the secondary windingby leads 45 and 4'! respectively, as shown in the diagram of Fig. 2.Electrodes 48, 50 correspond in every way to electrodes 29, 22 of Figs.1 and 2, and electrodes 44, 46 function, like glectrode 24, to ionizegas in the sealed envelope It will be seen that the protective device ofthe invention provides a simple and inexpensive means for protectingtransformers, particularly of the type used in neon sign Work, frombecoming damaged by breakage of the sign to which the transformer isconnected.

The invention is hereinbefore described and illustrated in preferredforms, but it is to be understood that the scope'of the invention is notin any way limited by this illustrative showing but only as indicated bythe scope of the appended claims.

Iclaim:

1. A protective means for connection into a transformer circuit havingan overload fuse in it primary circuit, comprising a container filledwith ionizable gas, leads connected across said primary circuit and eachterminating in an electrode within the container, said electrodes beingspaced apart a distance sufficient to provide a spark gap across whichan arc may not occur when said gas is not ionized, and means operable inresponse to excessive voltage in said secondary circuit to ionize saidgas and thereby reduce the resistance to arcing across said gap.

2. The device of cla m 1 wherein the last named means comprises a leadconnected into one leg of said secondary circuit and terminating in athird electrode exposed to the gas within the container and operable inconiunction with one of said primary circuit connected electrodes inresponse to said excessive voltage to ionize said gas.

3. An electrical circuit having a transformer comprising a primarycircuit and a secondary circuit, an overload fuse, in the primarycircuit, and means in the primary circuit to cause blowing of the fusein response to excessive voltage in said secondary circuit, including: asealed container filled with inonizable gas, a pair of leads connectedinto the primary circuit and each terminating in an electrode within thecontainer, said electrodes being spaced apart to provide a gas filledspark gap therebetween of sufficient width to prevent arcing thereacrosswhen the gas is not ionized, and electrode means exposed to said gas andoperable in response to excessive voltage in the secondary circuit toionize said gas. said last named electrode means being connected intothe secondary circuit.

4. A protective means for connection into a transformer circuit havingan overload fuse in its primary circuit, including a secondary triggeredtwin d ode comprising a container filled with ionizable gas, a firstpair of spaced elecrodes and a second pair of spaced electrodes in saidcontainer, leads connecting said first pair of electrodes across theprimary circuit of the tran former, leads connecting said second pair ofelectrodes across the secondary circuit of the transformer, said firstand said second pair of electrodes being spaced apart a d stancesufficient such that ionization of the gas does not occur under ordinaryoperating voltages of the transformer and said first pair of electrodesbeing spaced apart to provide a spark gap therebetween of sufiicientWidth to prevent arcing thereacross when the gas is not ionized, saidsecond pair of electrodes being operable in response to excessivevoltage in said secondary circuit to ionize said gas and thereby reduceresistance to arcing across said gap.

RICHARD H. SEAMAN.

(References on following page) REFERENCES CITED The following referencesare of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Stokes July 17, 1928 Niemann July1, 1930 Boudion May 24, 1932 Bieger Mar. 8, 1932 Young Aug. 30, 1932Evans June 5, 1934 Number Number

